Lithography system

ABSTRACT

A maskless lithography system for transferring a pattern onto the surface of a target. At least one beam generator for generating a plurality of beamlets. A plurality of modulators modulate the magnitude of a beamlet, and a control unit controls of the modulators. The control unit generates and delivers pattern data to the modulators for controlling the magnitude of each individual beamlet. The control unit includes at least one data storage for storing the pattern data, at least one readout unit for reading out the data from the data storage, at least one data converter for converting the data that is read out from the data storage into at least one modulated light beam, and at least one optical transmitter for transmitting the at least one modulated light beam to the modulation modulators.

The present application is a divisional of non-provisional U.S. patentapplication Ser. No. 10/692,632 filed Oct. 24, 2003, now U.S. Pat. No.6,958,804 issued Oct. 25, 2005, which claims priority from U.S.Provisional application No. 60/421,464 filed Oct. 25, 2002.

BACKGROUND

Lithography systems, including ion, laser, EUV and electron beamsystems, all require means to process and deliver a pattern to some kindof writing means. A well known way to accomplish this is by using amask, and projecting this mask onto a substrate. As the resolutionbecomes smaller and smaller, these masks have become more difficult toproduce. Furthermore, the (optical) means for projecting these maskshave become very complex.

A way of to overcome this problem is by using maskless lithography.

Maskless lithography systems can be divided in two classes. In the firstclass the pattern data are sent towards the individual radiation sourceor sources. By tuning the intensity of the sources at the right times, apattern can be generated on the substrate, which is most often a waferor a mask. The switching of sources may get problematic when theswitching speed increases, for instance due to a settling time or asource, which can be too long.

The second class of maskless lithography systems on the other handcomprises either continuous sources or sources operating at constantfrequency. The pattern data are now sent towards modulation means, whichcompletely or partly stop the emitted beams from reaching the targetexposure surface when necessary. By controlling these modulation meanswhile moving over the target exposure surface, a pattern is written. Themodulation means are less critical for settling times. A lot of masklesslithography systems designed to achieve a higher throughput aretherefore using modulation means.

In U.S. Pat. No. 5,834,783, U.S. Pat. No. 5,905,267 and U.S. Pat. No.5,981,954, for instance, a maskless electron beam lithography systemwith one electron source is disclosed. The emitted electron beam isexpanded, collimated and additionally split by an aperture array into aplurality of beamlets. A blanker array fed with pattern data stops theindividual beamlets when a control signal is given. The obtained imageis then reduced by a reduction electron optical system and projected ona wafer.

In US-A-1-20010028042, US-A-1-20010028043, US-A-1-20010028044,WO-A1-02/054465, WO-A1-02/058118 and WO-A1-02/058119, a masklesselectron beam lithography system using a plurality of electron sourcesis disclosed. The emitted electron beamlets pass a blanker array, whichdeflects the individual electron beamlets when the appropriate controlsignal is given. The electron beams are shaped by a shaping array, andfocused on a wafer.

In WO-01/18606 and U.S. Pat. No. 6,285,488 an optical lithography systemis disclosed which uses a spatial light modulator (SLM) to modulate alight beam. A light source emits light pulses directed towards the SLM.The SLM comprises an array of deformable mirrors, which reflect theemitted beam towards a substrate or towards a beam stop structuredepending on a control signal sent to the mirror involved.

The current invention is based on the following insight andunderstanding of the fundamentals of lithography.

A mask is a highly efficient way to store a pattern, the amount of rawdata to describe a pattern is enormous. Moreover, for a commerciallyacceptable throughput, the data must be transported towards the writingmeans at a very high data rate. Additionally the high data rate must beobtained within limited space. It was up to now not recognized thatimprovement of the data path in maskless lithography systems has aprofound effect on the through-put of these Systems.

The information on a mask is normally used to transfer a pattern fromthe mask on a certain area on the target exposure surface. This area iscalled a die. To get an idea of the amount of data that has to betransferred, imagine a die of 32 mm by 26 mm.

Now consider that somebody wants to write a pattern with a criticaldimension (CD) of 45 nm. Then there are 4.1*10¹¹ CD-elements on a die.If each CD element consists of at least 30*30 pixels to satisfy therequirements, and if there is only one bit needed to represent theintensity of said pixel, the information present on a mask isrepresented by about 3.7*10¹⁴ bits. Say a commercially acceptablethroughput for a maskless lithography system is about 10 wafers/hr. Ifthere are 60 dies on a wafer, 60 times 3.7*10¹⁴ bits have to betransported towards the modulation means per wafer. So 600 times3.7*10¹⁴ bits have to be transported towards the modulation means in3600 seconds to get the desired throughput. This corresponds to a datatransfer rate of about 60 Tbit/s!

In all mentioned systems the control signals are sent electronicallytowards the modulation means. However, the bandwidth of a metal wire islimited. The limit on the bandwidth of an electrical interconnect isrelated to the maximum total capacity of an electrical interconnectB_(max), to the overall cross-section A and the length of the electricalinterconnect L in the following way:B _(max) =B ₀* (A/L ²)

The constant of proportionality B₀ is related to the resistivity ofcopper interconnects. For typical multichip module (MCM) technologies B₀is about 10¹⁶ bit/s. For on-chip lines its value is about 10¹⁶ bit/s.The values are almost independent on the particular fabricationtechnology.

The limit on the bandwidth of the electrical interconnect is furthermoreindependent of its configuration. Whether the interconnect is made up ofmany slow wires or a few fast wires up to the point where other effectstart to limit the performance makes no difference.

The desired total capacity of the electrical interconnect is100*10¹²=10¹⁴ bit/s. This corresponds to a ratio of the overallcross-section to the square of the length of the electrical interconnector 10⁻¹ in the case of a MCM and 10⁻² in the case of an on-chipconnection. So if L is 1 m., the overall cross-section of the copperthat is needed is 0.01-0.1 m²! Compare that number with the size of adie that is written, which is 0.0008 m², and it is evidently impossibleto establish the data transfer without a demagnification of at least 10after the pattern information is added to the light beam.

Another approach to visualize the problem is to use the typical speed ofan electrical interconnect, which is in the order of 1 Gbit/s. So totransfer 100 Tbit/s, 100,000 copper wires are needed! This takes anenormous amount of space and is difficult to handle.

SUMMARY OF THE INVENTION

An objective of the current invention is to improve the systemsdescribed above.

A further objective of the current invention is to increase thethroughput of a maskless lithography system.

A further objective or the current invention is to reduce thesensitivity of the lithography system with respect to all kinds of(electromagnetic) disturbances.

A further objective of the current invention is to reduce the spaceneeded for transferring pattern data into the lithography system.

A further objective of the current invention is to increase designflexibility of the system.

The invention therefore provides a maskless lithography system fortransferring a pattern onto a surface of a target, comprising:

at least one beam generator for generating a plurality of beamlets;

a modulation means comprising a plurality of modulators for modulatingthe magnitude of a beamlet and

a control unit for controlling each modulator,

wherein the control unit generates and delivers pattern data to saidmodulation means for controlling the magnitude of each individualbeamlet, the control unit comprising:

at least one data storage for storing the pattern data;

at least one readout unit to read out the pattern data from the datastorage;

at least one data converter for converting the pattern data read outfrom the data storage into at least one modulated light beam;

at least one optical transmitter for transmitting said at least onemodulated light beam to said modulation means.

Using optical data transportation in a lithography system makes itpossible to create a maskless lithography system based on knowntechnology, but having an increased though-put. Furthermore, it ispossible to reduce the area needed. Furthermore, optical transmissionoffers additional freedom for designing the layout of the lithographysystem.

The radiation source that can be used in the beam generator can emit anykind of radiation like electrons, positrons, x-rays, photons or ions.The source is either a continuous source or a source that is pulsed witha continuous frequency. The source therefore does not generate anyinformation. However, the purpose of a lithography system is to patterna certain target exposure surface. Since the source does not provide anypattern data or pattern information, the pattern information has to beadded to the beamlets somewhere along their trajectory by modulationmeans. It should in this invention be realized that the patterninformation is transported using an optical system. The patterninformation is used to control modulation means which modulates beamletswhich actually write the pattern into a resist or in another waytransfer the pattern onto a sample, for instance a semiconductor wafer.In the system, the nature or the pattern writing beamlets depends on thenature of the source. In fact, the modulated light beam is a patterninformation carrying light beam, and the beamlets are pattern writingbeamlets.

In an embodiment, the beam generator has only one source, and thelithography system has only one beam generator. In this way, it iseasier to control the inter beamlet homogeneity of the system.

The modulation means can operate in different ways and be based onvarious physical principles, depending on the nature of the beamletsused for writing the pattern. It may generate a signal which results inthe activation of some blocking mechanism which stops the beamlet, forinstance a mechanical shutter or a crystal becoming opaque due toelectro-acoustic stimulation. Another possibility is that to have themodulation means selectively generate a signal, which results in theactivation of some sort of deflector element, like an electrostaticdeflector or a mirror. This results in a deflection of the selectedirradiated beamlet. The deflected beam is then projected on a blankerelement, for instance a beam absorbing plate provided with apertures,aligned with the deflectors of mirrors. In both cases a commerciallysatisfactory throughput can only be acquired when the beamlet modulationis done very fast, preferably with a frequency of 100 MHz or more.

In maskless lithography systems the pattern information or pattern datais represented by computer data, generally digital computer data. Thepattern data is partially or completely stored in the data storage ofthe control unit. The control unit therefore comprises a data storagemedium, e.g. RAM, hard disks or optical disk. This data is stored in aformat that can be used to control the modulation means in such a waythat a predetermined pattern can be repetitively generated. Furthermore,the control unit comprises means to read out the data at a high datarate, To establish the high data rate the control unit comprises anelement that converts the data into at least one pattern data carryinglight beam. In an embodiment, this data converter a vertical cavitysurface emitting laser (VCSEL) diode. If a bit is one, a light signal isemitted while no light is sent out if the value of the bit equals zero.By reading out a sequence of bits, a pattern information carrying lightbeam is created. The pattern information carrying light beams are thentransported towards the modulation means. There are several possiblecarriers that can realize the data transfer. In an embodiment, paralleldata storage means are used which are read out almost simultaneously inorder to obtain the data rate required.

In an embodiment the transfer from the converter element in the controlunit a region close to the modulation means achieved using opticalfibers for the data transport. This allows flexible data transport withminimal disturbance by electromagnetic fields and other means.Furthermore, at allows the control unit to be located remote from therest of the lithography system, for instance between 2-200 meters awayfrom the rest of the system.

Currently, optical fibers that are used in telecom and Ethernetapplications are optimized for specific wavelengths, predominantly 850,1300 and 1500 nm. The 850 nm optimization is established due to the goodavailability of the standard InGaAs/GaAs laser diodes. The infraredwavelengths are used because of the low fiber transmission losses,typically smaller than 0.4 dB/km. Future developments aim forwavelengths of 660 and 780 nm. The lower wavelengths are preferred forthe present invention because of fewer diffraction related limitationsat these wavelengths. However, in some configurations larger wavelengthsare desired. The wavelengths that can be used in the present inventionrange from about 200 to 1700 nm. Current developments furthermore makeit possible to transfer multiple signals through one channel. For thispurposes either multi-wavelength or multi mode optical fibers aredeveloped, and multiplexing/demultiplexing techniques are used.Preferably, for the wavelength of the modulated light beams is selectedin an area which interferes as little as possible with the beamlets andwith the rest of the system. This allows the optical transmitter to bedesigned almost independently from the rest of the lithography system.

In an embodiment of the invention, each modulator or the modulationmeans comprises a light sensitive element for converting said at leastone modulated light beam coming from said control unit into a signal foractuating said modulator. In this way, the optical transmitter can bekept small. The transfer rates can be very high, and the modulator canfor instance be made using lithographic technologies. In a furtherembodiment thereof, said optical transmitter comprise at least oneoptical fiber having a modulation means end and a control unit end, fortransmitting said at least one modulated light beam from said controlunit to said modulation means.

In an embodiment, the lithography system comprises at least oneprojector for projecting said at least one modulated light beam on saidmodulation means. In this way, it offers an even greater freedom ofdesign. Furthermore, interference can be reduced.

In an embodiment with optical fibers, said at least one optical fiber atits modulation means end is coupled to one or more optical fiber arrays.In a further embodiment thereof, substantially each optical fiber fromsaid one or more optical fiber arrays is coupled to one of said lightsensitive converter elements.

In an alternative embodiment, said at least one optical fiber at itsmodulation means end is coupled to one or more optical waveguides, andsaid optical waveguides being coupled to the light sensitive elements.

In an embodiment of the maskless lithography system described above,said optical transmitter comprises at least one multiplexer at itscontrol unit end and at least one demultiplexer at its modulation meansend.

In another embodiment of the maskless lithography system describedabove, the system has an optical path parallel to which said pluralityof beamlets are traveling, wherein said optical transmitter isfurthermore provided with optical coupler for coupling said at least onemodulated light beam into said optical path.

In embodiment described above, the data converter and the opticaltransmitter is adapted for generating at least one modulated light beamhaving at least one wavelength between 200 and 1700 nm. This wavelengthwas found to interfere as little as possible with the rest of thesystem. Furthermore, it allows use of many of-the-shelf components usedin optical telecommunication applications.

In a further embodiment of the invention, each light sensitive elementis provided with a selection filter which is transparent for apredetermined wavelength range, or a selection filter for transmittinglight having a predetermined direction of polarization, or a prism whichlimits the sensitivity of said light sensitive element to light enteringsaid prism from a predetermined direction, or a grating which limits thesensitivity of said light sensitive element to light entering saidgrating from a predetermined direction. In this way, x-talk can bereduced.

In a further embodiment of the maskless lithography system comprisingoptical fibers, said light sensitive element comprises a photodiode, inan embodiment a MSM-photodiode, a PIN-photodiode or an avalanchephotodiode.

In an embodiment of the maskless lithography system with an opticalfiber array, the modulator comprises an electrostatic deflector.Especially when the beam is a charged particle beam, this allows easymodulation, using parts which are well known in other fields oftechnology.

In an embodiment of the maskless lithography system according to thepresent invention, the data converter comprises a laser diode.

In an embodiment, the optical transmitter comprises at least one opticalfiber having a modulation means end and a control unit end, fortransmitting said at least one modulated light beam from said controlunit to said modulation means, and at least one projector for projectingsaid modulation means end of said optical fiber or optical fibers onsaid modulation mean. In this way, a flexible design of the system ispossible, both in lay-out and in choice of components.

In an embodiment, each modulator of the modulation means comprises alight sensitive element for converting said at least one modulated lightbeam coming from said control unit into a signal for actuating saidmodulator, and said modulation means has a beam generating means sideand a target side.

In an embodiment, each of said modulators comprise at least oneelectrostatic deflector, an aperture between said at least oneelectrostatic deflector and said target side, said electrostaticdeflectors of said modulators defining an electrostatic deflector arrayand said apertures of said modulators defining an aperture array.

In a further embodiment, each electrostatic deflector is operationallycoupled to a light sensitive element.

In this embodiment, said optical transmitter comprises at least one beamsplitter for splitting said at least one modulated light beam into aplurality of modulated light beams.

In a further embodiment, the optical transmitter comprises projectorsfor projecting said plurality of modulated light beams on said lightsensitive elements.

In this embodiment, said projector are adapted for projecting at anangle between 0 and 88 degrees relative to a plane perpendicular to saidelectrostatic deflector array. In this embodiment. In a furtherembodiment, the projector comprises at least one lens for projecting theplurality of modulated light beams on said electrostatic deflectoraperture array.

In an embodiment, the projector comprise a first demagnifier with areduction optical system for demagnifying the plurality of modulatedlight beams and a projection optical system for projecting thedemagnified plurality of modulated light beams on said electrostaticdeflector aperture array. In an embodiment thereof, said reductionoptical system comprises a micro lens array, each micro lens of saidmicro lens array being aligned with one of said plurality of modulatedlight beams and adapted for reducing the size of said one of saidmodulated light beams. In a further embodiment thereof, said projectionoptical system further comprises a mirror, for reflecting the pluralityof modulated, demagnified light beams coming from the reduction opticalsystem in the direction of said lens of the projection optical system.

In an embodiment of the electron beam maskless lithography systemdescribed above, the area on the modulation means not covered by thelight sensitive elements is provided with a reflective layer.

In an embodiment of the electron beam maskless lithography systemdescribed above, a diffusive layer is provided on the surface of themodulation means facing the incoming plurality of modulated light beams.

In an embodiment, said optical transmitter further comprises an opticalwaveguide for coupling each of the plurality of modulated light beamssubstantially parallel to the electrostatic deflector aperture arrayplane towards its corresponding light sensitive element. In a furtherembodiment thereof, the optical transmission means further comprises anoptical micro lens array provided with a plurality of micro lenses, eachmicro lens being aligned with one of said plurality of modulated lightbeams for coupling its modulated light beam into a corresponding opticalwaveguide.

In an embodiment, the optical transmitter comprises a plurality ofoptical fibers, the data converter means comprising means for couplingsaid at least one modulated light beam in said plurality of opticalfibers, said plurality of optical fibers being grouped to form at leastone fiber ribbon, said at least one fiber ribbon being attached at oneof the sides of said electrostatic deflection array, and the lightsensitive elements being adapted for electrically activating theircorresponding electrostatic deflector via electrical interconnects.

In another embodiment, the maskless lithography system, the generatingmeans comprise light beam generating means. In an embodiment thereof,the light generating means are adapted for generating a light beamhaving a wavelength smaller than 300 nm. In a further embodimentthereof, the modulation means comprises a spatial light modulator. In afurther embodiment thereof, the spatial light modulator comprises adeformable mirror device, comprising an array of micro-mirrors. In yet afurther embodiment thereof, each micro-mirror comprises a lightsensitive element mounted on its backside coupled to said opticaltransmission means for receiving a modulated light beam.

The invention further relates to a process wherein a masklesslithography system is used described above.

The invention further relates to a method for transferring a patternonto the surface of a target using a lithography system comprising beamgenerator for generating a plurality of beamlets and modulation meansfor individually controllably modulating substantially each beamlet,said method comprising: retrieving pattern data from data storage;transforming said pattern data into at last one modulated light beam;optically coupling said at least one modulated light beam to saidmodulation means.

In an embodiment of this method the modulation means comprise an arrayof modulators, each provided with light sensitive elements, and methodfurther comprises: directing said at least one modulated light beam ontosaid modulators; coupling each of said modulated light beams to onelight sensitive element.

DRAWINGS

The invention will be further elucidated in the following embodiments ofa maskless lithography system according to the current invention, inwhich:

FIGS. 1A, 1B a an operation scheme of part of the system of theinvention,

FIGS. 2A, 2B, 2C free space optical coupling,

FIGS. 3A, 3B illumination schemes of a modulation means,

FIG. 4 projection of optical fiber array on modulation array;

FIGS. 5A, 5B projection systems for projecting a pattern informationcarrying light beam on modulation means,

FIGS. 6A-6D illuminating schemes for the light sensitive elements,

FIG. 7 coupling of pattern information carrying light beams to lightsensitive elements,

FIG. 8 top-view or FIG. 7,

FIG. 9 optical coupling using optical fiber ribbons,

FIG. 10 modulation means for an electron beam lithography system,

FIG. 11 free space coupling of pattern information carrying light beamsto modulation means,

FIG. 12 illumination scheme of a modulation means,

FIG. 13 maskless optical lithography system,

FIG. 14 projection of fiber ends on modulation means

DETAILED DESCRIPTION OF THE INVENTION

Since the modulation means are fed with an optical signal, they eachcomprise a light sensitive clement, preferably a photodiode. The basicoperation of the modulation means is schematically shown in FIG. 1A.FIG. 1 a schematically shows the basic operational steps performed bythe modulation means. Each modulation means is provided with a lightsensitive element, preferably a photodiode, to be able to receive anoptical signal.

If the light sensitive element receives light, a signal is generated andsent to modulator. As a result the passing beamlet will be modulated andnot reach the target exposure surface. If there is no light, there is nosignal transferred to the modulator. The beamlet passes undisturbed, andfinally reaches the target exposure surface. By moving the targetexposure surface and the rest of the lithography system relative to eachother while sending pattern information towards the modulation means, apattern can be written.

It is of course also possible to operate the whole system in theopposite way as shown. In FIG. 1B. In this case light falling on thelight sensitive element results in the cancellation of the signal senttowards the modulation means. The passing beamlet will reach the targetexposure surface without any modulation. However, when the lightsensitive element does not receive light, a signal is sent towards themodulation means, which prevents the passing beamlet from reaching thetarget exposure surface.

The attachment of the optical fibers to the modulation means can giveserious complications. In an embodiment of the present invention, thelast part or the data trajectory therefore uses a different transfermedium. In the latter case the fibers terminate closely packed thusforming an optical fiber array. The emitted pattern information carryinglight beams are then sent towards other optical carriers. When themodulation means are located in a vacuum, it might be preferable to keepthe optical fibers outside the vacuum. In this case the emitted lightbeams can for instance couple into the lithography system via atransparent part of the vacuum boundary.

In most cases it is not practical to bring the pattern informationcarrying light beams all the way to the light sensitive elements throughoptical fibers. In that case other optical carriers can continue thedata transfer. Preferably the optical fibers are bonded together to forman optical fiber array. The pattern information carrying light beamsthen travel towards the light sensitive elements in a different way. Onepossible way of data transfer is to send the light emitted from thefibers towards the light sensitive elements of the modulation meansthrough the same environment as wherein the irradiated beamlets aretraveling. In this way free space optical interconnects are created.Another possible transport medium is an optical wave-guide, which islocated in the structure of the modulation means.

In the case of an optical wave-guide or an optical fiber, multiplewavelengths can be transported through the channels as is commonly donein telecommunication applications. The space occupied by the transfermedium then reduces significantly, because several pattern informationcarrying light beams share the same channel. The conversion towards asignal that can be used by the modulators can be made with anopto-electronic receiver, like a DWDM multi-wavelength receiver.

The light sensitive element can be any element known in the art thatconverts an incoming light signal into any other kind of signal, like anelectric or an acoustic signal. Examples of such converters are photocathodes, phototransistors, photo resistances and photodiodes. In orderto meet the high data rate requirements, the light sensitive elementshould have a low capacitance, enabling it to operate at a highfrequency. Moreover the element is preferably easy to integrate in themodulation means. There are photodiodes that meet the demands mentionedabove. The preferred embodiment uses an MSM-photodiode. The mainadvantage of this photodiode is its low capacitance. It is thereforeable to operate at a high frequency. Moreover, the fabrication of aMSM-photodiode is relatively easy. Another good option would be the useof a PIN-photodiode. This element also has a low capacitance, but it issomewhat more difficult to integrate this component in an array. Anothervery useful option is an avalanche photodiode.

As mentioned earlier, the data rate and thus the required modulationfrequency are very large. In order to be able to modulate at this rate,suitable switching circuitry is important. Besides the three opticalcarriers, which will be discussed below, other related means to transfermodulated light beams are embodied by the present invention.

Transfer Options

Free Space Optical Interconnects

When the pattern information carrying light beams are projected on thecorresponding light sensitive elements through the same medium aswherein the irradiated beamlets are traveling, several complicationsarise. It is often not possible to project the pattern informationcarrying light beams on the light sensitive elements perpendicular tothe plane wherein the light sensitive element is located. This can forinstance be the case when the irradiated beamlets are already projectedperpendicular to said plane. The interference between the beamlet andthe pattern information carrying light beam might have an influence onthe pattern, which results in an incorrect data transfer from controlunit towards target exposure surface. To avoid this problem the patterninformation carrying light beams reach the light sensitive surface ofthe light sensitive element, say a photodiode, at a certain angleHowever, when this angle of incidence a increases, the spot size of thepattern information carrying light beams on the light sensitive surfaceof the photodiode increases as well. In order to address each photodiodeindividually, the spot size of the pattern information carrying lightbeams should be less than the light sensitive surface area or thephotodiode. The angle of incidence .alpha. should therefore be as smallas possible. However, this is not always possible due to obstacles asshown in FIG. 2A.

With a smart choice of the location of both fiber array 2 and obstacle1, some of the problems may be avoided. However, this is not alwayspossible. The present invention includes ways to reduce the angle ofincidence .alpha. without removal or replacement of the obstacle 1. Afirst option is to make the obstacle 1 transparent for the patterninformation carrying light beams. If the barrier is for instance anelectrostatic lens array, it can for instance be made of some kind ofconductive glass or polymer. Alternatively, the wavelength of thepattern information carrying light beams can be chosen in such a waythat the obstacle 1 becomes transparent for these beams. Silicon, forinstance, becomes transparent for wavelengths larger than 1100 nm. Sowhen a standard fiber wavelength of 1500 nm is used, the emitted beamswill pass the silicon barrier without noticing its existence.

Another possibility to reduce the angle of incidence .alpha. withoutremoving the obstacle 1 is to use more optical fiber arrays 2. In FIG.2A a situation is sketched wherein the pattern information carryinglight beams leaving the fiber array 2 are projected on a plate 3 coveredwith modulators. The emitted beams cover the total plate 3. If in thisconfiguration the projected spot size is too large, the angle ofincidence can be reduced by moving the fiber array 2 away from themodulation means plate 3 perpendicular to the plane wherein thephotodiodes are deposited as is shown in FIG. 2B. As a result thecritical angle of incidence .alpha 1 is reduced. Now the spot size maybe limited within the requirements. However, only half of the plate 3 isilluminated. By using a second fiber array 2 at the same height at theopposite side of the modulation plate 3 as shown in FIG. 2C, the entireplate 3 is illuminated and the spot size is small enough. Both opticalfiber arrays 2 comprise halt the amount of fibers compared to theoriginal one. By selecting the right amount of optical fiber arrays 2, aplate provided with an array of light sensitive elements can beilluminated with the desired angle of incidence .alpha₁.

FIGS. 3A and 3B show a top view of a squared and a rectangularmodulation plate 3. The dotted lines bound the area illuminated by onefiber array. As already explained earlier, one fiber array may not beenough. In that case for instance 2, 4 or 6 optical fiber arrays 2 canbe used to illuminate the entire plate within the requirements.

Furthermore it is possible to couple the pattern information carryinglight beams into the system via some reflections. The obstacle 1 can forinstance be coated with a reflective material. Moreover additionalmirrors can be placed on strategic positions in the system to create thedesired angle of incidence.

The pattern information carrying light beam has a diameter of about50-150 μm when a multi mode optical fiber is used. A single mode fiber,on the other hand, only has a diameter of about 1-10 μm. The lightsensitive surface of a photodiode can be in the order of 10-30 micronssquared.

In an embodiment, multi mode optical fibers are used, so the diameter ofthe pattern information carrying light beams leaving the optical fiberarray needs to be reduced. Furthermore some kind of focusing has to bearranged to realize projection with the correct resolution.

An optical assembly may be needed to perform both reduction and focusingof the pattern information carrying light beams. There are severalproperties of the light beams that can easily be modified. The diameterof the light beams leaving the optical fiber array 2 can be demagnified,and/or the distance between two adjacent light beams, the so-calledpitch, can be reduced by optical means.

Focusing light beams leaving the optical fiber array 2 on the modulationplate 3 can most easily be achieved when both optical fiber array 2 andmodulation array 3 are lying parallel to each other. If the two planesare not parallel the spot size of each individual light beam on themodulation array 3 will vary. The projection of the fiber array 2 on themodulation plate 3 is done with a lens 5. Often the light beams areprojected on the modulation plate 3 with an angle of incidence unequalto zero. The optical fibers 4 in the optical fiber array 2 may then bearranged in such a way that the light beam leaving the optical fiber isdirected towards the lens as is shown in FIG. 4. In this way asufficient illumination of the lens s is ensured.

When the lens 5 is located exactly in the middle between the opticalfiber array 2 and modulation plate 3, 1:1 projection takes place. Movingthe lens towards the modulation plate 3 reduces both diameter and pitchof the pattern information carrying light beams. Moving the lens 5 inthe other direction, i.e. in the direction of the optical fiber array 2,will result in an increase of both parameters.

For an optimum performance regarding both reduction and projection morelenses may be needed. A possible configuration with two lenses 6 and 7is shown in FIG. 5A. The entire image and thereby the diameter of eachindividual pattern information carrying light beam 8 leaving the opticalfiber array 2 is reduced. In an embodiment with obstacles, mirrors canbe used to project the light beams on the light sensitive elements.

In some cases the beam diameter needs to be reduced more than the pitchbetween the adjacent light beams. In FIG. 5B, an alternative embodimentis shown. In this embodiment, a micro lens array 9 positioned betweenthe optical fiber array 2 and a projection lens 7 can arrange this. Eachindividual lens of the micro lens array corresponds to a single fiber 4in the optical fiber array 2. The diameter of each pattern informationcarrying light beam 8 leaving the optical fiber array 2 is individuallydemagnified in this configuration as depicted in FIG. 5B. A projectionlens 7 focuses all the demagnified beams onto the corresponding lightsensitive elements. When direct projection is impossible due to someobstacle, mirrors can be used to project the pattern informationcarrying light beams on the light sensitive elements at the desiredangle of incidence .alpha..

Another potential problem related to the spot size, cross talk betweenadjacent pattern information carrying light beams emitted from the fiberarray 2, can be reduced by applying several measures. Consider againthat the beams are projected on an array of modulation means wherein thelight sensitive surfaces of for instance photodiodes are all lyingwithin one plane at one side of the array.

A solution to this cross talk problem is depicted in FIG. 6A. The areabetween adjacent light sensitive elements is covered with a reflectivelayer 10. The major part of the incoming light beam falls on the lightsensitive converter element 11. The part of the light beam that is notfalling on the element 11 is reflected back into the system, withoutaffecting any of the adjacent elements. Coating the light sensitiveelements 11 with an anti-reflective layer can enhance the lightdetection efficiency even further.

Cross talk can also be reduced using a diffusive layer 12 on top of theentire array 3, as shown in FIG. 6B. The incoming light is now scatteredin all directions. Due to scattering, the light intensity of thereflected beam drops dramatically.

Yet another way to reduce the cross talk is to use a filter located ontop of the light sensitive converter element 11. Examples are awavelength filter 13 as shown in FIG. 6C, or a polarization filter. Thewavelength filter 13 enhances the selectivity for a certain wavelength.As a result, waves coming from adjacent patterned beams with a slightlydifferent wavelength are filtered out. A filter only transmitting lightpolarized in a predetermined direction works has the same effect.

Yet another possible measure is to make the light sensitive elements 11only sensitive for light coming from a predetermined direction, forinstance by incorporating small prisms 14 or gratings 15 in themodulation array 3 as depicted in FIG. 6D. Only the light falling on thelight sensitive element 11 at the correct angle and coming from theright direction is used in the modulation process. Light coming from allother directions is excluded.

Optical Wave-Guides

A second possibility to transfer the pattern information carrying lightbeams leaving the optical fiber array 2 towards the light sensitiveelements 11 embedded in the modulation means is the use of planaroptical wave-guides. Planar optical wave-guides can be thought of asoptical fibers embedded into or onto a substrate. Consider again thearray of modulation means 3. When planar optical wave-guides areintegrated in this array, a system as schematically shown in FIG. 7 isconstructed. Each individual pattern information carrying light beam 8leaving the optical fiber array 2 has to be coupled into thecorresponding optical wave-guide 16 directly or via an array of lenses17 as shown in FIG. 7. Each lens then couples an individual patterninformation carrying light beam 8 into the entrance point of thecorresponding planar optical wave-guide 16. The optical wave-guide 16transports the pattern information carrying light beam 8 through themodulation array 3 towards the correct light sensitive element 11. Thelight sensitive element 11 converts the pattern information carryinglight beam 8 into a sequence of signals, which activate or deactivatethe modulators 18. Consequently the incoming beamlet will be controlledaccording to the pattern information. The sequence of signals in thisembodiment is transported through electric wires 19 embedded in themodulation array 3 towards the modulators 18.

FIG. 8 shows a top view of the same configuration as depicted in FIG. 7.In this case two fiber arrays 2 are used to control all the modulators18. However, any number of arrays 2 is applicable. The light sensitiveelements 11 are represented by squares, the modulators 18 by circles.Only two trajectories of pattern information carrying light beams 8 areshown for clarity reasons.

Optical Fibers

A third possibility for the data transfer from the control unit towardslight sensitive element 11 is to use optical fibers for the entiretrajectory. The major problem with this approach is the connection ofthe individual fibers 4 to the structure wherein the modulation meansare integrated. Again imagine that a modulation array 3 is used.Connecting the individual fibers 4 to this array 3 may give problemswhen for instance this array 3 is moving for scanning purposes.Mechanisms like stress and friction are introduced in the region ofattachment. Eventually the connection can break. This can be avoided bycombining a group of optical fibers 4 to form a fiber ribbon 20. Theribbon 20 is then connected at the side of the modulation array 3 asshown in FIG. 9, showing only two ribbons 20. Another number of ribbons20 is also possible. Two exemplary trajectories of optical fibers withinthe fiber ribbon are schematically shown with dashed lines. The lightsensitive elements 11, represented in the figure as squares, may belocated close to the contact of the fiber ribbon 20 with the modulationarray 3, but they may also be located closer to the incoming beamlets.Preferably the optical signals are converted in electric signals. Thesesignals are transported through on chip electric wires 19 towards themodulators 19, represented by circles, located in close proximity of thecorresponding incoming irradiated beamlets. The drawing only shows anumber of the modulators present on the modulation array 3.

EXAMPLES

The next two sections describe two examples of maskless lithographysystems embodied by the present invention.

Example 1 Maskless Electron Beam Lithography System (FIG. 10)

In the maskless electron beam lithography system used in this example,the system comprises an aperture plate comprising electrostaticdeflectors 21 to deflect incoming electron beamlets 22 passing throughthe apertures 23. This plate will be referred to as the beamlet blankerarray 24. When the electron beamlets 22 have passed the beamlet blankerarray 24 they will reach a second aperture array (beam stop array) 25 onwhich their trajectory will terminate when they are deflected.

The modulation concept of this lithography system is shown in FIG. 10.Incoming electron beamlets 22 are projected on the beamlet blanker array24. The positions of the electron beamlets 22 correspond to thepositions of the apertures 23 in the plate 24. The beamlet blanker plate24 comprises a deflector element as modulation means. In this examplesaid deflector element comprises an electrostatic deflector 21.Depending on the received information the deflector 21 located in thebeam blanker array 24 will be turned on or off. When the deflector 21 isturned on, an electric field is established across the aperture 23,which results in a deflection of the beamlet 22 passing this aperture23. The deflected electron beamlet 27 will then be stopped by thebeamlet stop array 25. In this case no information will reach the targetexposure surface When the deflector 21 is turned off the beamlet will betransmitted. Each transmitted beamlet 28 will be focused on the targetexposure surface. By moving the target exposure surface and the assemblyof arrays relatively to one another and by scanning the beamlets withfor instance an additional beamlet deflector array a pattern can bewritten.

FIG. 11 shows a possible configuration of the usage of free spaceinterconnects in this maskless lithography system. The patterninformation carrying light beams B coming out of and leaving the opticalfiber array 2 of the optical transmitter are demagnified by two lenses29. Alternatively also other configurations as for instance shown inFIG. 5 can be used. The pattern information carrying light beams 8 arethen projected on the beamlet blanker plate 24 with a mirror 30 and afocusing lens 7. The angle or incidence .alpha. ranges from 0 and 80degrees. If .alpha. is larger than 80 degrees or a smaller angle isdesired due to other complications the beamlet blanker plate 24 can beilluminated with more than one fiber array 2 as is shown in FIG. 12. Inthe depicted situation of FIG. 12, 4 fiber arrays 2 illuminate thebeamlet blanker plate 24. In FIG. 12 the 4 corresponding focusing lenses7 are depicted, focusing the pattern information carrying light beams 8on the respective part of the beamlet blanker plate 24.

Example 2 Maskless Optical Lithography System (FIG. 13)

The maskless lithography system in this example comprises a spatiallight modulator (SLM) 40. Maskless lithography systems using an SLM arein a general way disclosed in WO 0118606. The SLM comprises an array ofmirrors, which reflect the incoming light beams in such a way that thebeam eventually is blanked or transmitted. An example of such an SLM isa deformable mirror device (DMD). A DMD is controlled in the same way asthe electrostatic deflector array shown in the first example. Themodulation signals couple into the system from the back or from theside.

One configuration is a backside control of the modulation. By providingthe backside of each mirror with a light sensitive element, the controlcan be done with the use of the same optical carriers as mentionedbefore. Probably the use of free space optical interconnects is the mostconvenient option.

A schematic drawing of the operation is shown in FIG. 13. A laser 41emits a light beam 42, which is split into a plurality of beamlets 44 bya beam splitter 43. The plurality of beamlets 44 is projected on the SLM40. Pattern information carrying light beams 46 sent from the controlunit 45 to the SLM 40 control the transmission probability of beamlets44 coming from the beam splitter 43. The transmitted beamlets 47 arefocused on the target exposure surface 49 using lens 48 (which can alsobe a lens system).

By moving the target exposure surface 49 and the rest of the systemrelatively to each other a pattern can be written.

In FIG. 14, an overall side view is shown of a lithography system inwhich the modulation means ends 2 of optical fibers are projected anmodulator array 24 using optical system 54, represented by lenses 54.Modulated light beams 8 from each optical fiber end are projected on alight sensitive element of a modulator. In particular, ends of thefibers are projected on the modulator array. Each light beam 8 holds apart of the pattern data for controlling one or more modulators.

FIG. 14 also shows a beam generator 50, which generates a beam 50. Usingan optical system 52, this beam is shaped into a parallel beam. Theparallel beam impinges on beam splitter 53, resulting in a plurality ofsubstantially parallel beamlets 22, directed to modulation array 24.

Using the modulators in the modulation array 24, beamlets 27 aredeflected away from the optical axis O of the system and beamlets 28pass the modulators undeflected.

Using a beam stop array 25, the deflected beamlets 27 are stopped.

The beamlets 28 passing stop array 25 are deflected at deflector array56 in a first writing direction, and the cross section of each beamletis reduced using projection lenses 55. During writing, the targetsurface 49 moves with respect to the rest of the system in a secondwriting direction.

The lithography system furthermore comprises a control unit 60comprising data storage 61, a read out unit 62 and data converter 63.The control unit is located remote from the rest of the system, forinstance outside the inner part of a clean room. Using optical fibers,modulated light beams holding pattern data are transmitted to aprojector 54 which projects the ends of the fibers on to the modulationarray 24.

It is to be understood that the above description is included toillustrate the operation of the preferred embodiments and is not meantto limit the scope of the invention.

The scope of the invention is to be limited only by the followingclaims. From the above discussion, many variations will be apparent toone skilled in the art that would yet be encompassed by the spirit andscope of the present invention.

1-41. (canceled)
 42. A maskless lithography system for transferring apattern onto the surface of a target, comprising: a beam generatingmeans for generating a plurality of beamlets; a modulation meanscomprising a plurality of modulators wherein each modulator is adaptedfor modulating the magnitude of a beamlet; and a control unit forcontrolling each of the modulators, wherein the control unit producesand delivers pattern data to said modulation means for controlling themagnitude of each individual beamlet, the control unit comprising: anoptical transmitter for transmitting at least one modulated light beam,carrying modulation data for modulating said beamlets, to saidmodulation means, said optical transmitter comprising an opticalwaveguide structure integrated with a structure for said modulationmeans for transporting the pattern information carrying light beamtowards a respective light sensitive element of said modulators forconverting such coupled light signal into an electrical signal foractuating the related beamlet modulator.
 43. The system according toclaim 42, wherein said optical waveguide structure is embedded into oronto a substrate.
 44. The system according to claim 43, wherein thesubstrate comprises said plurality of modulators.
 45. The systemaccording to claim 42, wherein said plurality of modulators is includedin a planar array.
 46. The system according to claim 42, wherein eachmodulator of the modulation means comprises a light sensitive element.47. The system according to claim 46, wherein the optical waveguidestructure comprises a plurality of waveguides, said optical waveguidesbeing coupled to the light sensitive elements.
 48. The system accordingto claim 42, wherein the optical transmitter comprising coupling meansfor coupling the modulated light beams into said waveguide structure.49. The system according to claim 48, wherein the coupling meanscomprises an array of lenses, wherein each lens is arranged for couplingan individual pattern information carrying light beam into an entrancepoint of a corresponding optical waveguide.
 50. The system according toclaim 42, wherein said optical transmitter further comprises at leastone optical fiber or an optical fiber array, each individual patterninformation carrying light beam leaving the at least one optical fiberor an optical fiber of the optical fiber array is coupled into an acorresponding optical waveguide.
 51. The system according to claim 50,wherein two or more fiber arrays are used for controlling all of themodulators of the systems.
 52. The system according to claim 50, whereina group of optical fibers form a fiber ribbon which is connected to theside of the modulation array.
 53. The system according to the precedingclaim, wherein the light sensitive elements are located close to thecontact of the fibre ribbon.
 54. The system according to claim 50,wherein substantially every optical fiber from said one or more opticalfiber arrays is coupled to one of said light sensitive converterelements.
 55. The system according to claim 50, wherein said at leastone optical fiber at its modulation means end is coupled to one or moreoptical wave-guides, and said optical wave-guides being coupled to thelight sensitive elements.
 56. The system according to claim 42, whereinsaid optical transmission means comprise at least one multiplexer at itscontrol means end and at least one demultiplexer at its modulation meansend.
 57. The system according to claims 42, having an optical pathparallel to which said plurality of beamlets are traveling, wherein saidoptical transmission means are furthermore provided with opticalcoupling means for coupling said at least one modulated light beam intosaid optical path.
 58. The system according to claim 42, wherein theoptical transmitter is adapted for generating at least one modulatedlight beam having at least one wavelength between 200 and 1700 nm. 59.The system according to claim 42, wherein each light sensitive elementis provided with a filter selected from the group comprising a selectionfilter which is transparent for a predetermined wavelength range, aselection filter for transmitting light having a predetermined directionof polarization, a prism for limiting the sensitivity of said lightsensitive element to light entering said prism from a predetermineddirection, and a grating for limiting the sensitivity of said lightsensitive element to light entering said grating from a predetermineddirection.
 60. The system according to claim 42, wherein said lightsensitive element comprises a photodiode.
 61. The system according toclaim 60, wherein said photodiode is a MSM-photodiode, a PIN-photodiodeor an avalanche photodiode.
 62. The system according to claim 42,wherein said modulator comprises an electrostatic deflector.
 63. Thesystem according to claim 62, wherein said optical transmitter furthercomprises an optical wave guide for coupling each of a plurality ofmodulated light beams substantially parallel to the electrostaticdeflector aperture array plane towards its corresponding light sensitiveelement.
 64. The system according to claim 42, wherein said dataconverter comprises a laser diode.
 65. The system according to claim 42,wherein said beam generating means comprises an electron beam generatingmeans, an ion beam generating means or an x-ray beam generating means.66. The maskless lithography system according to claim 42, eachmodulator of the modulation means comprising a light sensitive elementfor converting said at least one modulated light beam coming from saidcontrol unit into a signal for actuating said modulator, said modulationmeans having a beam generating means side and a target side, each ofsaid modulators comprising at least one electrostatic deflector, anaperture between said at least one electrostatic deflector and saidtarget side, said electrostatic deflectors of said modulators making upan electrostatic deflector array and said apertures of said modulatorsmaking up an aperture array, each electrostatic deflector being coupledto a light sensitive element, the light sensitive elements being locatedat the beam generating side of said modulation means and saidelectrostatic deflectors being located between said light sensitiveelements and said aperture array.
 67. The system according to claim 66,wherein said optical transmission means comprise beam splitting meansfor splitting said at least one modulated light beam into a plurality ofmodulated light beams, and optical couplers for coupling each modulatedlight beam to a light sensitive element.
 68. The system of claim 67,wherein said optical couplers comprise projecting means for projectingsaid plurality of modulated light beams on said light sensitive elementsat an angle between 0 and 80 degrees relative to a plane perpendicularto said electrostatic deflector array.
 69. The system of claim 67,wherein said optical couplers comprise at least one lens for projectingthe plurality of modulated light beams on said electrostatic deflectoraperture array.
 70. The system according to claim 69, wherein theprojecting means comprise a first demagnifier with a reduction opticalsystem for demagnifying the plurality of modulated light beams and aprojection optical system for projecting the demagnified plurality ofmodulated light beams on said electrostatic deflector aperture array.71. The system according to claim 70, wherein said reduction opticalsystem comprises a micro lens array, each micro lens of said micro lensarray being aligned with one of said plurality of modulated light beamsand adapted for reducing the size of said one of said modulated lightbeams.
 72. The system according to claim 71, wherein said projectionoptical system further comprises a mirror, for reflecting the pluralityof modulated, demagnified light beams coming from the reduction opticalsystem in the direction of said lens of the projection optical system.73. The system according to claim 42, wherein the area on the modulationmeans not covered by the light sensitive elements is provided with areflective layer.
 74. The system according to claim 42, wherein adiffusive layer is provided on the surface of the modulation meansfacing the incoming plurality of modulated light beams.
 75. A processwherein a maskless lithography system is used according to claim
 42. 76.A method for transferring a pattern onto the surface of a target using alithography system comprising beam generating means for generating aplurality of beamlets and modulation means for individually controllablymodulating substantially each beamlet, said method comprising:retrieving pattern data from data storage means; transforming saidpattern data into at last one modulated light beam; optically couplingsaid at least one modulated light beam to said modulation means via anoptical transmitter for transmitting the at least one modulated lightbeam, carrying modulation data for modulating said beamlets, to saidmodulation means, said optical transmitter comprising an opticalwaveguide structure integrated with a structure for said modulationmeans for transporting the pattern information carrying light beamtowards a respective light sensitive element of said modulators forconverting such coupled light signal into an electrical signal foractuating the related beamlet modulator.
 77. The method of claim 76,wherein said modulation means comprise an array of modulators, eachprovided with light sensitive elements, the method further comprising:splitting said at least one modulated light beam into a plurality ofmodulated light beams; coupling each of said modulated light beams toone light sensitive element.